U3 KA4a - Cells Of The Nervous System Flashcards
What is the Cell body of a Nerve cell?
The cell body contains the nucleus and most of the cytoplasm. It is the control centre of cell metabolism
What is the axon of a Nerve cell?
An axon is a single nerve fibre that carries nerve impulses away from a cell body.
What are the dendrites of a Nerve cell?
Dendrites are nerve fibres which receive nerve impulses and pass them towards a cell body.
What is the path of a nerve impulse in a nerve cell?
Dendrites -> Cell Body -> Axon
What are the 3 types of neurons
Sensory, Interneurons and motor neurons
Describe the role of Sensory Neurones
Carry impulses into the Central Nervous System (CNS) from sense organs
Describe the role of Interneurones
Found in the CNS where they connect with other neurons
Describe the role of Motor Neurones
Carry impulses out from the CNS to effectors such as muscles and glands
What is the Myelin sheath?
Myelin is the fatty tissue that insulates an axon
What does the Myelin Sheath do?
The presence of myelin greatly increases the speed at which impulses can be transmitted
What is Myelination?
Myelination is the name given to the process of myelin developing round axon fibres
When is Myelination complete?
Myelination increases from birth to Adolesence
Certain diseases damage or destroy the myelin sheath causing…
a loss of co-ordination (due to slower impulses).
State the roles of Glial Cells
Some types of glial cells are responsible for myelination of neurons.
Some lay down tightly packed layers of plasma membrane around an axon.
Other glial cells act as a support for neurons. e.g. Producing chemicals the neurons need to function.
What is a Synapse?
A synapse is the tiny gap between an axon ending of one neuron and the dendrite of the next neuron in the pathway
What is the nerve cell before the synaptic cleft Called?
The presynaptic neuron
What is the nerve cell after the synaptic cleft Called?
Postsynaptic neuron
Describe the transmittion of a nerve impulse across the synaptic cleft
Neurotransmitters are stored in vesicles at each end of the presynaptic neuron (the presynaptic terminal).
When a nerve impulse arrives, the vesicles moves to fuse with the membrane of the neuron and release the neurotransmitter into the synaptic cleft
The neurotransmitters then diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane
What are Neurotransmitters stored in?
vesicles
Describe the direction of travel for neurotransmitters
Nerve impulses can only travel in one direction.
Why are neurotransmitters quickly removed from the synaptic cleft between impulses?
To prevent continuous stimulation of postsynaptic neurones
State 2 ways in which Neurotransmitters can be remover from the synaptic cleft
- Re-uptake
- Enzyme degradation
Describe the Re-uptake of Neurotransmitters
The neurotransmitter is reabsorbed directly back into the presynaptic membrane that secreted it.
It is then stored again in vesicles ready for use for future impulses
Describe the Enzyme Degradation at the synaptic cleft
The neurotransmitter is broken down by an enzyme to form non active products.
These products are then reabsorbed by the presynaptic neurone and re-synthesised into active neurotransmitter (packaged in vesicles)
What are the two types of signals received at the post synaptic neurone?
- Excitatory
- Inhibitory
Excitatory Signals…
increase impulses sent to effectors
Inhibitory Signals
decrease impulses sent to effectors
Why may a nerve impulse not be transmitted across the synapse?
Not enough neurotransmitter molecules were released - Threshold was not reached
What is summation?
A series of weak stimuli (from neighbouring neurones) combine to trigger enough neurotransmitter to fire an impulse in the post-synaptic neurone
